1. Field of the Invention
The present invention relates to vacuum pumps used in semiconductor manufacturing apparatus, and more particularly, the present invention relates to the structure of a vacuum pump for balancing a rotating body of the vacuum pump.
2. Description of the Related Art
In process such as dry etching, chemical vapor deposition (CVD), or the like performed in a high-vacuum process chamber in a semiconductor manufacturing step, a vacuum pump such as a turbo-molecular pump is used for producing a high vacuum in the process chamber by exhausting gas from the process chamber.
A rotating body of such a turbo-molecular pump is usually formed of an aluminum alloy. In the turbo-molecular pump used under severe circumstances, for example, exposure to a corrosive gas such as a gaseous chlorine or a fluorine sulfide gas, the aluminum-alloy rotating body has a corrosion-resistant film on the surface thereof, for example, coated by nonelectrolytic plating such as nickel-phosphor-alloy plating or the like.
The turbo-molecular pump as described above is required for balancing the rotating body rotating at high speed during its assembly process. A conventional way of finely balancing is performed by carving out of a part of the circumferential outer or inner surface of the rotating body with a drill or a router so as to change the mass of the rotating body.
According to the conventional way of balancing achieved by carving out of a part of the surface of the rotating body, since a drill or a router carves out a part of the corrosion-resistant film coated on the surface of the rotating body, the corresponding part of the aluminum alloy under the corrosion-resistant film is exposed to the outside and is accordingly subjected to corrosion. A stress corrosion crack of the carved part of the rotating body caused by the corrosion develops during the high speed rotation of the rotating body, and eventually results in the breaking of the rotating body in the worst case.
An alternative way of finely balancing the rotating body is achieved such that, instead of carving out of a part of the rotating body, a mass such as a weight is added to the surface of the rotating body having a corrosion-resistant film thereon so as to change the mass of the rotating body while preventing the rotating body from being corroded. However, according to the above-mentioned mass-addition way of balancing, the mass is likely to be flaked off from the surface of the rotating body due to the centrifugal force of the rotating body during at a high speed, thereby making it difficult to maintain the balance of the rotating body for a long period of time.
The present invention is made in view of the above-described problems. Accordingly, it is an object of the present invention to provide a vacuum pump in which a rotation body can avoid being broken due to corrosion and the balance thereof can be maintained for a long period of time.